Process for making d-glucuronic acid and its salts



' agitation; although thisis not absolutely Patented July 31, 1951 OFFICE PROCESS FOR MAKING D-GLUCURONIO AcmANn ITS SALTS Charles L. Mehltretter, Peoria, 111., assignor to the United States of America as represented bythe Secretary of Agriculture 7 .No Drawing. Application April 24, 1950,

' I SerialNo. 157,841

Claims.

d Granted under the act of March 3, 1883, as.

v Q." 1 7 This application is made under the act of March 3, 1883, as amended-by the act of April 30, 1928, and the invention herein described, if patented in any country, may be manufactured and used by or for the Government of the United States of America; for governmental purposes throughoutthe worldwithout the payment-to me of any royalty thereon. r This. invention relates to a method for prepar- -ing D-glucuroni c acid and-its salts by catalytic oxidation of alphamethyl-D-glucoside.- Accordqato ,thepresent invention, alpha-methyl-D- glucoside is oxidized in the presence of a catalyst to alpha-methyl-D-glucuronoside. The latter compound is subsequently hydrolyzed, preferably as the crude oxidation mixture, by'mineral acids to produce a mixture of organic acids containing ipre'do'minately D-glucuronic acid. I

The invention also includes the recovery of D-glucuronic acid fromthe crude hydrolysis mixture by crystallization as its alkali metalor ammonium aniline N-D-glucuronoside. The alkali metal or ammonium salt of D-glucuronic acid is readily obtained by heating an acidified aqueous ,solution of the'correspondingsalt of aniline N-D- ,glucuronoside. This liberates the'aniline which -ma ylbe removed by extraction ,with a selective solvent, such as ether or be'nze nen Alternatively, .the'recovery. step may beeffected by treating the salt of aniline N-D-glucuronoside with benzaldezhyde to form benzal-aniline which is readily re- ;moved by extraction. 1

In the recoverystepsnoted inthe foregoing paragraph the Deglucuronate salt isgpresent in the; aqueous layer, separate from the aniline layer, and maybe recovered therefrom by known 'methodspas for example; byevaporationand crystallization. It can be converted into D-elucuronic acid, by known methods, if desired.

According to my invention: alpha-methyl-D- glucoside in aqueous solution is oxidized by means of an oxygen-containing gas; such as oxygen or amended April 30, 1928; 370' 0. G. 757) such'as sulfuric acid, for reasons of convenience. The acidified solution is then concentrated to dryness, preferably at a temperature below- 50 C. Alpha-methyl-D-glucuronoside and .other sugar acids-present in the residue are then extracted with a selective solvent, as for example hot methanol or ethanol to separate these acids from the residual mineral salt. The extract is subsequently evaporated in. vacuo to a sirup.

The separation of the residual mineral salt, composed of the cation of the alkali added during the oxidation and the anion of the mineral acid subsequently added, may take place during the later steps, but it-is convenient to do so immediately upon liberation of the free organic acids as 7 described above.

air. The oxidation process is carried out at pI-I 4,-9.5, maintained by 'the addition of alkali, in the presenceof a platinum, preferably aplatimum-activated carbon catalyst. The tempera- -ture employed may vary over awide range, as for example, room temperature up to..70 CI. andthe :reaction is benefited by continuous and'vigorous necessay, a The product isa mixturecomprising the salt} {of alpha methyl D glucuronoside; This 'mixtureis then acidified to pH 1.5-2 witha suitable aci d." I prefera' non-oxidizing'mineral acid,

The sirup, freed of mineral salt, is then hydrolyzed with a suitable acid, preferably anonoxidizing mineral acid. The" resulting hydrolysate is composed of 'D-glucuronicacid =admixedwith other sugar acids. One of the featuresof my, process, and anintegral part thereof, is the recovery of the D-glucuronate salt in the pure state from this crude acid hydrolysate. I accomplish this recovery by means of the aniline ,N D-glucuronoside salt.

Thehydrolysate may be evaporated to a small volume for convenience in handling. It is then neutralized-with an alkaline agent and treated with a molecular excess of aniline. At this point the pH of the mixture may be adjusted toe-5 with acid to facilitate the precipitation of aniline N-D-glucuronoside salt. The precipitation may be further facilitated by the addition of ethanol. The salt is then separated by decantation or filtration.

The alkaline agent used to neutralize the crude lacid hydrolysate containing glucuronie acid may be an oxide, hydroxidefcarbonate' or bicarbonate of an alkali-metal or ammonia. "The cation'of this base isth e cation of the aniline N-D-glucuronosi-de salt, and of the glucur'onate salt finally recovered. For reasons of convenience I prefer 'aceticacid to split away the aniline by hydrolysis.

The freed aniline is removed from the solution 'by-ext'raction with a suitable solvent such as "ether.

The raffinate is an aqueous solution containing the glucuronate salt. This salt may. be

tion of benzal-aniline, which may then be re- 7 moved by extraction.

The following specific examples illustrate the invention.

EXAMPLE 1 Thirty-five grams of alpha-methyl-D-glucoside were dissolved in a liter of water in a 3 -l iter creased flask. To this solution was added 15.1 grams of sodium bicarbonate and after it haddlssolved 7 grams of platinum-activated carbon catalyst containing 13 percent platinum was introduced. The mixture, was vigorously stirred at 50 C. and air passed through at the rate of 112 liters per hour. After 25 hours the pH of the reaction mixture was 6.7. The catalyst was then removed by filtration and washed with water. Thefiltrate and washings were concentrated in vacuo to about 300 cc. and treated with 4 N sulfuric acid to obtain pH 2. The acidified solution was concentrated to dryness in vacuo at a bath temperature below 50 C. The residue was extracted with hot methanol and after removal of the methanol by vacuum evaporation, yielded 41.2 grams of sirup containing the free sugar acids formed in the oxidation.

A solution of 5.3 grams of the sirup in 50 cc. of N sulfuric acid was heated at 95-l00 C. in a steam bath for 15 hours. The hydrolysis mixture was diluted to 100 cc. with water. partially decolorized with carbon and the sulfuric acid precipitated as barium sulfate by the addition of 7 .9 grams of barium hydroxide octahydrate. The

barium sulfate was filtered off, washed with water 1 and the filtrate and washings combined and .concentrated in vacuo to about 10 cc. The residual sirup was neutralized with sodium hydroxide solution and a solution of 3.5 'cc. of aniline in 20 cc. of ethanol added. Fifty co. more of ethanol was added and the solution adjusted to pH 4 with glacial acetic acid. After addition of 100 cc. of ethanol crystallization of sodium aniline 'N-D-glucuronoside began. After standing at 10 C. overnight the crude product was removed by Three and fiveetenths grams of sodium aniline N-D-glucuronoside prepared as in Example 1 was dissolved in 15 cc. of water and 0.5 cc. of glacial acetic acid introduced. The solution-was heated at90 C. for 10 minutes, and immediately I water,

'-curonoside, neutralizing the hydrolysate thereby causin the p ec ita io of. an ne ND. elucoronqside sa a d reco ering from said .b acid hydrqlysh iysglueurcnic aci lt extracted with ether to remove aniline. The water layer was filtered from a small amount of insoluble matter and the residue washed with The combined filtrate and washings (5 0 1 1 5 c wer irredand tre ted -.with 250 cc. of ethanol and then 25 cc. of acetone, when sodium D-glucuronate crystallized out. The

product was filtered and washed with 95 percent ethanol. After drying at C. it weighed 2.9 grams. It had the following analysis:

Found: Na 9.8 Caled. for: Na 9.8 'CsHao'lNa H2O Reducing value by the Munson-Walker method showed product to be 100 percent sodium D- glucuronate monohydrate.

Method B Six grams of sodium aniline N-D-glucuronoside, prepared as in Example 1, were dissolved in 25 cc. of water and 5 cc. of benzaldeh-yde added. The mixture was heated at 100 C. forhour with a reflux condenser attached to the flask. The mixture was cooled and the benzal, aniline form-ed together with excess benzaldehyde removed by ether extraction. The water layer containing the sodium D-glucuronate was concentrated in vacuo to about 20 cc. To this was added 400 cc. of methanol and 100 cc. of acetone. The precipitated white sodium D-glucurcnate monohydra-te was removed by filtration, washed with acetone, and air dried. Yield, 4.3 grams. it had the following analysis: 4

Found: Na,9.8; C 31.5; 34,9 al d. r: Na 9.8; C 0. H 4. CGHQO'zNa'HZO Analysis of the product :by the Mimsonewalker method showed it to be 99.4% pure.

EXAMPLE 3 PREPARATION or SODIUM ANILINE N-D-mucmzorvosmn Ten grams of D-glycuronolactone were dis solved i n20 cc. of water and made slightly alkaline with 4 N sodium hydroxide solution. To the yellow-colored solution was added with stirring a solution of 15 cc. of aniline in 35 cc. of 95 percent ethanol. Crystallization of sodium aniline N-D- glycuronoside soon began. About 5 cc. of glacial acetic acid were added to acidify the mixtureand greater crystallization occurred. After standing at room temperature for 15 minutes and at 10 C. for 1 hr., the product was filtered off and washed with methanol. After drying at C., it weighed 11.0 grams (crop 1). Another crop of 0.5 gram crystallized from the combined mother liquor and washings.

Analysis of crop 1, dried 58/Inm. 4 hrs.

Found: Na 7.9; .N 1.8 Galcd. for: Na 7.9; N 4,8

C12 I:I1 4O6N a I claim: 7 1. The method which comprises oxidizingby means of free oxygen-containing gas alpha-:- methyl-D-glucoside in the presence of a catalyst, hydrolyzing with acid the resulting oxidation mixture containing alpha-methyly-n glntreatin th neutralized hyd lysa with-an rating the thus precipitated aniline N-D-glu curonoside, hydrolyzing with acid the separated aniline N-D-glucuronoside, removing the freed aniline from the reaction mixture, whereby an aqueous solution containing D-glucuronic acid salt remains and recovering said D-glucuronic acid salt.

3. The method which comprises oxidizing at 'pH 4 to 9.5. by means of free oxygen-containing gas alpha-methyl-D-glucoside in the presence of a platinum-activated carbon catalyst, hydrolyzing with a non-oxidizing mineral acid the resulting oxidation mixture containing alphamethyl-D-glucuronoside, neutralizing the hydrolysate, separating mineral salt from the hydrolysate by selective extraction, treating the hydrolysate. with aniline at pH 4-5, separating the thus precipitated aniline N-D-glucuronoside, hydrolyzing with acid the separated aniline N-D- glucuronoside, removing the freed aniline from the reaction mixture, whereby an aqueous solussues 6 tion containing D-glucuronic acid salt remains and recovering said D-glucuronic acid salt.

4. A process of preparing sodium-D-glucuronate comprising heating aqueous sodium aniline N-D-glucuronoside with benzaldehyde, extracting the benzal-aniline formed with ether, and precipitating the sodium-D-glucuronate monohydrate from the aqueous solution with methanol and acetone.

5. A process comprising oxidizing alphamethyl-D-glucoside with molecular oxygen containing gas in the presence of platinum-activated carbon catalyst at pH 4 to 9.5, maintained by addition of alkali, acidifying, extracting alpha-methyl-D-glucuronoside, removing mineral salt, and hydrolyzing with acid to yield D- glucuronic acid;

CHARLES L. MEHLTRETTER.

REFERENCES CITED UNITED STATES PATENTS Name Date Peterman Aug. 29, 1950 OTHER REFERENCES Weygand, Ber. 723, 1663-1667 (1939).

Number 

1. THE METHOD WHICH COMPRISES OXIDIZING BY MEANS OF FREE OXYGEN-CONTAINING GAS ALPHAMETHYL-D-GLUCOSIDE IN THE PRESENCE OF A CATALYST, HYDROLYZING WITH ACID THE RESULTING OXIDATION MIXTURE CONTAINING ALPHA-METHYL-D-GLUCURONOSIDE, NEUTRALIZING THE HYDROLSATE AND TREATING THE NEUTRALIZED HYDROLYSATE WTIH ANILINE THEREBY CAUSING THE PRECIPITATION OF ANILINE N-DGLUCORONOSIDE SALT AND RECOVERING FROM SAID SALT BY ACID HYDROLYSIS D-GLUCURONIC ACID SALT. 